The invention relates to image fixing in electrophotography, and is specifically concerned with a roller for heat-fixing a toner image on a support sheet and method of producing the same.
The most efficient way of fixing a toner image is to heat the image by pressing the support sheet against a heating roller to thereby fix the image by fusion or melt adhesion. One disadvantage of such fixing is the so-called "offset phenomenon". This phenomenon occurs when the toner particles forming the image are rendered tacky by heating, and portions of the toner image adhere to the periphery of the heating roller, and are thereby transferred onto the successive sheet or sheets which come in contact with the roller. The cycle is repeated, and results in copies of poor quality.
Several means have been devised to preclude or reduce the effects of this offset phenomenon. For example, the radially outward surface of the rollers used for heat fixing of toner images has been made of materials which are very hard. Silicon oil has been applied to the radially outward surface to provide a protective coating and to prolong the service life of the roller. However, when there is no silicon oil coating, or when there are discontinuities in the silicon oil coating, the radially outward surface of such rollers tends to deteriorate and their service life tends to be shortened because of the heat to which the rollers are exposed and because of the friction between the rollers and the toner image bearing sheets.